Download Application Note: Multiple Display Load Isolation Using the FSAV330 Appl icat

Application Note: Multiple Display Load Isolation Using
the FSAV330
As PC gaming, video editing and DVD playback becomes
more popular, there exists an increased demand to display
PC graphics onto larger TV screens (instead of CRT monitors) or onto multiple CRTs. PC graphics cards are now
offering products to meet this demand. In addition, graphics chips have integrated composite video encoding (e.g.,
NTSC) and digital video interfaces (DVI).
An issue that graphics card designers will e ncounter in a
multi-display environment is th at of increased loading of
the video RAMDAC output. Display colors are determined
by specific voltage levels from the DAC in to 37.5Ω (75Ω
doubly terminated) per the RS-343 standard. Adding terminations and/or large RON analog switches would require
the use of additional buffer/amplifiers driving up cost a nd
complexity.
Increasing this load will not only violate graphics chip specifications but will deteriorate the video signal quality resulting in dim, unfocused and/or incorrect color images due to
improper voltage levels from the DAC. Image ghosting can
also occur due to the possible impedance mismatch seen
by the DAC output.
One way to accommodate multiple, simultaneously connected displays to a single graphics chip or video DAC is
through the use of a low-power, high-bandwidth, low-RON
analog video switch such as the FSAV330. The FSAV330
is a 4-channel Analog Video Switch and provides the ideal
solution for simple switching in, or isolating from, the 75Ω
display load. With a flat RON of 3Ω and a bandwidth in
excess of 18 0 MHz, the FSAV330 provides an i deal solution.
Application Note: Multiple Display Load Isolation Using the FSAV330
January 2002
Revised January 2002
Fairchild does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and
Fairchild reserves the right at any time without notice to change said circuitry and specifications.
LIFE SUPPORT POLICY
FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN L IFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD
SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or systems
which, (a) are intended for surgical implant into the
body, or (b) support or sustain life, and (c) whose failure
to perform when properly used in accordance with
instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the
user.
© 2002 Fairchild Semiconductor Corporation
2. A critical component in any component of a life support
device or system whose failure to perform can be reasonably expected to cause the failure of the life support
device or system, or to affect its safety or effectiveness.
AN500726
Print form created on January 7, 2002 1:39 pm
www.fairchildsemi.com
www.fairchildsemi.com